intel/dump_gpu: Fix corner cases in PPGTT range calculations

intel/dump_gpu: Fix corner cases in PPGTT range calculations

For large buffers which span an entire l1 page table, we got the range
calculations wrong.  In this case, we end up with an l1_start which is
the first byte represented by the given l1 table and an l1_end which is
the first byte after the range represented by the l1 table.  Then
l2_start_index == L2_index(l2_end) due to roll-over.  Instead, compute
lN_end using (1Ull << shift) - 1 so that lN_end is the last byte in the
range represented by the Nth level page table.  When we do this, we
don't need the conditional expression anymore.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>